let arr1 = ["abc"];             //相当于 let arr1:string[] = ["abc"];
let arr2 = [123];               //相当于 let arr2:number[] = [123];
let arr3 = ["abc",123,true];    //相当于 let arr1:(string | number | boolean)[] = ["abc",123,true];
arr3.push('bcd',534,false);
console.log(arr3);